In many cases, a blood filter device such as an arterial filter is incorporated in an artificial heart-lung circuit used for heart surgery involving extracorporeal circulation for the sake of safety. To provide security for patients, it has been demanded strongly that such a blood filter device be configured so that it can remove minute foreign substances in the artificial heart-lung circuit, thrombi formed during operation, or air that has entered or been released from the circuit so as not to allow them to enter the patient body.
A filter generally used in the blood filter device is a polyester screen filter with pores of about 20 to 40 μm that has been pleated and then formed into a cylindrical shape. For example, Patent Document 1 discloses that a filter sheet is folded so as to have a plurality of pleats and the pleated filter member then is formed into a cylindrical shape in which the respective pleats are arranged radially with peaks thereof positioned on the outer circumference side and valleys thereof positioned on the inner circumference side. The thus-formed cylindrical filter is disposed in a cylindrical housing. In the filter configured as above, blood flows in the housing in the radial direction of the cylindrical filter member to pass therethrough, which allows therethrough, which allows dirt, impurities, thrombi, and the like contained in the blood to be removed effectively.
In the filter as described above, blood first flows into an upper part of the cylindrical filter member, passes through the cylindrical filter member in its radial direction via an outer part of the filter member, and then flows out from a lower part of the cylindrical filter member via an inner part of the filter member. In this filter, the filter member surface extends vertically. This poses a problem in that, when a priming solution flows into the filter surface during a priming operation, air bubbles are liable to remain in the filter. Moreover, it is difficult to discharge the remaining air bubbles to the outside. This is because, since the filter member surface extends vertically, the air bubbles cannot be released from the filter easily, so that it takes quite a long time to remove the air bubbles completely.
More specifically, air bubbles remaining in the filter can be released with an impact from the outside caused by, for instance, flicking the housing with a finger. In this case, however, although the air bubbles can be released temporarily by giving an impact from a portion close to a position where the air bubbles adhere, they are liable to adhere again to an adjacent pleat of the filter. Thus, it is difficult to bring the air bubbles to an air vent provided above.
Patent Document 2 describes a blood filter device that solves such problems, and it is configured so that impurities, thrombi, and the like in blood can be removed effectively, and air bubbles remaining in a filter also can be removed easily.
The blood filter device described in Patent Document 2 includes a housing that includes a dome provided with a blood inlet and an air vent at the top of the dome, a filter retaining portion disposed below the dome, and a bottom portion that is disposed below the filter retaining portion and is provided with a blood outlet. Blood that has flowed into the dome from the inlet passes through the filter retaining portion, and flows out from the outlet. A filter is disposed in the filter retaining portion so as to partition a cavity of the housing into a dome side and a bottom portion side. The filter is formed of a sheet-like filter member folded to have a plurality of pleats, and it is disposed so that ridgelines of the plurality of pleats traverse respectively the cavity of the filter retaining portion in parallel.
According to this configuration, foreign substances, thrombi, and the like in blood can be removed reliably, and since there are no obstacles in the vertical direction of the filter, air bubbles adhered onto the top face of the filter during a priming operation can be removed easily by only applying a physical impact to the housing.    Patent Document 1: Japanese Patent No. 3270193    Patent Document 2: WO2004/084974